Some industrial processes, such as those in the petroleum industry, employ liquid holding vessels for various purposes, including for the separation of liquids having different specific gravities. Such vessels generally have a known or expected inflow value, and need to be periodically drained, or “dumped”, in order to maintain the liquid level in the vessel at or around a desired level. For much of their history, process control systems employed pneumatic level controllers and pneumatically actuated “dump” valves (or “drain” valves) for this purpose. Pneumatic control typically has very low latency, as the pressures employed in such control are capable of actuating a valve very quickly, for example, in as a few a hundred milliseconds.
Over time, process control systems have moved from pneumatic to electric control. In many instances, dump valves are electrically actuated and/or employ electric level controllers. Electric level controllers and, especially, electric actuators introduce latencies between the instruction to open or close a valve and the response of the actuator. For example, electric level controllers provide electric control signals which, if coupled to a pneumatic actuator, must be converted into a pneumatic signal to control a valve, and if coupled to an electric actuator must be acted upon by an electric motor that cannot actuate a valve as quickly as a pneumatic force. Accordingly, there is a delay between the time at which a sensor signal indicates to the level controller that a valve must be actuated, and the time at which the actuator responds to a command from the level controller.